half-life

  1. Noun.  (physics) The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.
  2. Noun.  (chemistry) In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value.
  3. Noun.  (medicine) The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity.
  4. Noun.  The time it takes for an idea or a fashion to lose half of its influential power.

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This entry was last updated on RefTopia from its source on 3/20/2012.